Add workflow to manage repository labels

[mcdonnnj]

🗣 Description

This pull request adds a new GitHub Actions workflow and configuration file to manage repository labels.

💭 Motivation and context

This adds a new workflow using the crazy-max/ghaction-github-labeler Action to manage a repository's labels. This will ensure that any repository derived from a skeleton has a consistent starting set of labels. Per-repository labels can then be layered in using this same configuration to ensure they are consistent. The labels in the configuration file are based on the configured labels in cisagov/.github.

This workflow is currently only run on changes to the configuration file or the workflow. We could also configure it to run on changes to labels per the documentation.

🧪 Testing

Automated tests pass.

✅ Pre-approval checklist

• [x] This PR has an informative and human-readable title.
• [x] Changes are limited to a single goal - eschew scope creep!
• [x] All relevant type-of-change labels have been added.
• [x] I have read the CONTRIBUTING document.
• [x] These code changes follow cisagov code standards.
• [x] All new and existing tests pass.

✅ Post-merge checklist

• [x] Archive Delete cisagov/github-label-management
• [x] Close https://github.com/cisagov/.github/pull/29

[mcdonnnj]

Great! Once this is merged we can archive cisagov/github-label-management, correct?

Yep. I will also close https://github.com/cisagov/.github/pull/29 as it is no longer needed.

Edit: Added those two tasks as post-merge items

[jsf9k]

Requesting re-review from @dav3r since I removed a duplicate label and added a new one. @mcdonnnj, can you also take a look?